In general, a probe card is an apparatus to be used in testing semiconductor devices such as a semiconductor memory, a display and the like during or after a manufacturing process thereof. In particular, the probe card electrically connects a wafer with a semiconductor test apparatus to transmit electrical signals from the semiconductor test apparatus to the semiconductor devices formed on the wafer and, also, to transmit response signals from the semiconductor devices to the semiconductor test apparatus so that the semiconductor devices can be tested.
The probe card includes a plurality of probe tips. Recently, as the size of the semiconductor device is getting smaller, the size of pads on a wafer chip and the distance (pitch) between the pads are also getting smaller. Therefore, various researches and developments are being actively conducted to miniaturize the probe tip which is brought into contact with the wafer chip.
FIGS. 1 to 9 are cross sectional views for describing a conventional procedure for fabricating a probe tip.
First, as shown in FIG. 1, a silicon nitride film 105 is formed on a silicon wafer 100.
Next, as shown in FIG. 2, a patterned photoresist layer 110 is formed on the silicon nitride film 105. At this time, the photoresist layer 110 is exposed by means of an ultraviolet exposure device or the like by using a mask layer (not shown) having a predefined pattern for forming the probe tip, and then a development process is performed on the exposed photoresist layer, so that the photoresist layer 110 can be patterned according to the pattern of the mask.
After that, as shown in FIG. 3, an exposed portion of the silicon nitride film 105 through the pattern of the photoresist layer 110 is etched by using a plasma device.
Then, as shown in FIG. 4, an ashing process or a wet strip process is performed to remove the patterned photoresist layer 110. Alternatively, an oxygen plasma process or a process employing a mixture solution of sulfuric acid and hydrogen peroxide can also be performed to remove the photoresist layer 110.
Subsequently, as shown in FIG. 5, the silicon wafer 100 having the silicon nitride film 105 formed thereon is dipped in a solution such as KOH, TMAH or the like capable of performing an anisotropic etching process on the silicon, whereby a trench 120 is formed as the silicon wafer 100 is etched.
Next, as shown in FIG. 6, the silicon nitride film 105 formed on the silicon wafer 100 is removed by using phosphoric acid or the like.
After that, as shown in FIG. 7, a photoresist layer 130 is formed on the entire surface of the silicon wafer 100 except a portion where the trench 120 is formed. Here, the thickness of the photoresist layer 130 determines the thickness of a body of the probe tip to be formed.
Then, as shown in FIG. 8, the trench 120 and an opening portion of the photoresist layer 130 are coated with Ni or a Ni alloy such as NiCo, NiFe, NiW or the like, so that a probe tip 140 is formed. After the coating process, a chemical mechanical polishing (CMP) process can be additionally performed to planarize the surface of the probe tip.
Finally, as shown in FIG. 9, the photoresist layer 130 is removed by performing the ashing process or the wet strip process, and the silicon wafer 100 remaining around the probe tip 140 is removed through a wet etching process so that the formation of the probe tip is completed.
At this time, since the silicon wafer used for fabricating the probe tip is generally a {100} silicon wafer, if the probe tip is fabricated in accordance with the conventional method, the front end of the probe tip would have an angle of only 54.7 degrees for a crystallographic reason.
As a result, as shown in FIGS. 10 and 11, assuming that ΔL is a difference between an initial height L1 of the front end of the probe tip 140 before worn out and a height L2 of a front end of a worn-out probe tip 140′, and ΔD is a difference between an initial surface size d1 of the front end of the probe tip 140 and a surface size d2 of the front end of the worn-out probe tip 140′, ΔD/ΔL increases rapidly. That is, the front end surface size of the probe tip rapidly increases as the probe tip is worn out, so that it is difficult to properly keep up with the miniaturization of pads on the wafer and a pitch therebetween. In other words, if the front end of the probe tip is not sharp enough, the problem related to the abrasion of the probe tip would become serious.
Meanwhile, in order to reduce the front end surface size of the probe tip to a predetermined size, a sanding process or other mechanical processes may be performed on the front end portion of the probe tip.
FIG. 12 is a plan view showing shapes of the front end of the probe tip before and after the probe tip is subjected to a machining process by a mechanical means. As shown in FIG. 12, a rectangular end surface shape of the probe tip can be turned into a square end surface shape through the mechanical process such as the sanding process.
However, in this case, though the surface size of the front end of the probe tip can be reduced, the fabrication accuracy through the sanding process and other mechanical processes notably deteriorates.
Accordingly, it is strongly requested to develop a technology capable of forming a probe tip with a sufficiently sharp front end for a probe card without having to perform the mechanical process such as the sanding process or the like.